1. Field of the Invention
The present invention relates to an electrode for a rechargeable lithium battery and a rechargeable lithium battery utilizing the same.
2. Description of Related Art
Battery characteristics of rechargeable lithium batteries recently under extensive development and research, such as charge-discharge voltage, charge-discharge cycle life characteristics and storage characteristics, depend largely upon the types of the electrodes used. This has led to the various attempts to better battery characteristics by improving electrode active materials.
The use of lithium metal as the negative active material enables construction of batteries which exhibit high energy densities per weight and volume. However, the lithium deposited on charge grows into dendrite, which could cause problematic internal short-circuiting.
On the other hand, rechargeable lithium batteries are reported using an electrode composed of aluminum, silicon, tin or the like which alloys electrochemically with lithium during charge (Solid State Ionics, 113-115, p57(1998)). Particularly among these, silicon has a high theoretical capacity and is a promising one as a high-capacity negative electrode for a battery. Accordingly, various rechargeable batteries have been proposed using this as a negative electrode (Japanese Patent Laid-Open No. Hei 10-255768). However, the negative electrodes composed of these types of alloys have failed to provide sufficient cycle characteristics since such alloys as electrode active materials are pulverized during charge and discharge to reduce their current collecting capabilities.
As an electrode for a rechargeable lithium battery which uses silicon or the like for an electrode active material and exhibits good charge-discharge cycle characteristics, an electrode has been proposed incorporating a microcrystalline or noncrystalline thin film deposited on a current collector by a thin-film forming technique such as a CVD or sputtering process (International Publication No. WO 01/31720A1).
In such an electrode for a rechargeable lithium battery, it has been found that the diffusion of a component of the current collector into the thin film of active material maintains good adhesion between the current collector and the thin film of active material to thereby improve charge-discharge cycle characteristics.
However, due to the improved adhesion between the current collector and the thin film of active material, the current collector elongates as the active material expands and shrinks during charge and discharge. This occasionally results in the occurrence of deformation, such as wrinkle formation in the electrode for a rechargeable lithium battery. The degree of deformation becomes greater particularly when a high-ductility metal foil such as a copper foil is used as the current collector. As the electrode undergoes deformation, its volume in the battery increases to problematically reduce an energy density per volume of the battery.